Astronomers Find Giant Collisional Ring Galaxy in Early Universe | Astronomy

Astronomers Find Giant Collisional Ring Galaxy in Early Universe | Astronomy

sci-news·2020-05-26 23:55

Astronomers have spotted a giant galaxy with a massive star-forming ring that existed 10.8 billion years ago.An artists impression of the collisional ring galaxy R5519. Image credit: James Josephides, Swinburne Astronomy Productions.Dubbed R5519, the ring galaxy was discovered in the systematic search for extremely distant spiral galaxies in the Cosmic Evolution Survey (COSMOS) field of the FourStar Galaxy Evolution Survey (ZFOURGE).Compared with our Milky Way Galaxy, it has a similar stellar mass, but has a radius that is 1.5-2.2 times larger and is forming stars 50 times faster.R5519 is a very curious object that weve never seen before. It looks strange and familiar at the same time, said Dr. Tiantian Yuan, an astronomer in the ARC Centre of Excellence for All Sky Astrophysics in 3 Dimensions (ASTRO 3D) and the Centre for Astrophysics and Supercomputing at Swinburne University of Technology.It is making stars at a rate 50 times greater than the Milky Way. Most of that activity is taking place on its ring — so it truly is a ring of fire.The team used images from the NASA/ESA Hubble Space Telescope and spectroscopic data from the MOSFIRE (Multi-Object Spectrograph for Infrared Exploration) and the OSIRIS (OH-Suppressing Infrared Integral Field Spectrograph) instruments at the W. M. Keck Observatory to make detailed measurements of R5519 and quantify its distance.The evidence suggests R5519 is a type known as a collisional ring galaxy, making it the first one ever located in the early Universe, the researchers said.There are two kinds of ring galaxies. The more common type forms because of internal processes. Collisional ones form as a result of immense and violent encounters with other galaxies.A composite image of the collisional ring galaxy R5519 and its environment compiled from Hubble and ZFOURGE images. Image credit: Tiantian Yuan / NASA / ESA / Hubble / ZFOURGE.Collisional ring galaxies are very rare in the present-day Universe. The Cartwheel Galaxy, the Arp-Madore 2026-424 system, and Arp 147 are all examples of ring galaxies thought to be formed by a collision of two galaxies.Contrary to previous predictions, the discovery of R5519 suggests that massive collisional rings were as rare 11 billion years ago as they are today.The collisional formation of ring galaxies requires a thin disk to be present in the victim galaxy before the collision occurs, said co-author Professor Kenneth Freeman, an astronomer in the Research School of Astronomy and Astrophysics at the Australian National University.The thin disk is the defining component of spiral galaxies: before it assembled, the galaxies were in a disorderly state, not yet recognisable as spiral galaxies.In the case of this ring galaxy, we are looking back into the early Universe by 11 billion years, into a time when thin disks were only just assembling. For comparison, the thin disk of our Milky Way began to come together only about 9 billion years ago.This discovery is an indication that disk assembly in spiral galaxies occurred over a more extended period than previously thought.The discovery is reported in a paper published this week in the journal Nature Astronomy._____T. Yuan et al. A giant galaxy in the young Universe with a massive ring. Nat Astron, published online May 25, 2020; doi: 10.1038/s41550-020-1102-7

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